1. Field of the Invention
The present invention relates generally to three-dimensional displays, and more particularly, to a three-dimensional display so adapted that a crosstalk region can be reduced to zero without decreasing brightness.
2. Description of the Prior Art
Typical examples of a three-dimensional display without glasses include a three-dimensional display by a parallax barrier method. In the three-dimensional display, a right eye image and a left eye image which are projected from an image projector such as an LCD (Liquid Crystal Display) projector are formed on a diffusing plate, and the formed images are viewed through a parallax barrier.
As shown in FIG. 14, right eye pixels R and left eye pixels L are alternately formed with portions where no image exists which is referred to as black portions 34 interposed therebetween on a diffusing plate 21, and each of the right eye pixels R is viewed with the right eye of a viewer and at the same time, each of the left eye pixels L is viewed with the left eye thereof through one of slits of a parallax barrier 22 arranged on the side of the viewer with respect to the diffusing plate 21, thereby to make it possible to view a three-dimensional image.
As shown in FIG. 15, a range 31 in which the right eye pixel R can be viewed and a range 32 in which the left eye pixel L can be viewed through one of the slits of the parallax barrier 22 are partially overlapped with each other. A range in which the right eye pixel R and the left eye pixel L can be viewed is referred to as a crosstalk region 33. If the eyes of the viewer enter the crosstalk region 33, it is impossible to view a three-dimensional image.
Since the crosstalk region 33 restricts the range of the lateral movement of the eyes which can view a three-dimensional image, it is preferable that there is no crosstalk region 33.
In order to reduce the crosstalk region 33 to zero, the range 31 in which the right eye pixel R can be viewed and the range 32 in which the left eye pixel L can be viewed in the position of the eyes of the viewer may be continuous without being overlapped with each other by making the width of the slit of the parallax barrier 22 smaller than that of the black portion 34.
In this three-dimensional display by a parallax barrier method, brightness per one pixel viewed is represented by .English Pound..multidot.x/w letting .English Pound. be the brightness of one pixel on the diffusing plate 21, x be a region where the eyes view a pixel aperture through the parallax barrier 22, and w be the width of the pixel aperture on the diffusing plate 21, as shown in FIG. 17.
If the width of the slit of the parallax barrier 22 is decreased so as to reduce the crosstalk region 33 to zero, x becomes small, whereby it is clear that the brightness per one pixel viewed is decreased.
In this three-dimensional display by a parallax barrier method, the change in brightness in a case where the viewer is moved rightward and leftward is such a change that in ranges 62 and 63 on the right and left sides centered with respect to a range 61 in which the maximum brightness .English Pound. is obtained, the brightness is gradually decreased as the viewer separates from the center, as shown in FIG. 18, because the width of each of the slits of the parallax barrier 22 is generally made larger than the width of each of the pixels R and L. In this case, the smaller the width of each of the pixels on the diffusing plate 21 is, the larger the range 61 is, and the smaller each of the ranges 62 and 63 is. If the viewer moves rightward and leftward, therefore, the brightness is less changed. As can be see from the foregoing, if sufficiently high brightness is obtained even if the ratio of each of pixel apertures is low in the parallax barrier method, it is the most suitable condition under which a three-dimensional image is viewed that the width of each of the black portions 34 on the diffusing plate 21 is as large as possible in the design in which there is no crosstalk region as shown in FIG. 16.
If an LCD projector is used as an image projector, however, the rate of the width of each of the black portions 34 of an image formed on the diffusing plate 21 corresponds to the rate of the width of a black matrix on an LCD panel in the LCD projector. If the width of each of the slits of the parallax barrier 22 is made smaller than that of each of the black portions 34 so as to reduce the crosstalk region 33 to zero, therefore, the ratio of the slit of the parallax barrier 22 is significantly reduced, whereby the utilization efficiency of light from a light source in the LCD projector is reduced.
It is considered that the ratio of each of the slits of the parallax barrier 22 is set to a value of not less than a predetermined value, and the width of each of the black portions 34 of the image formed on the diffusing plate is made larger than the width of each of the slits of the parallax barrier 22, thereby to reduce the crosstalk region 33 to zero.
Therefore, the rate of the width of each of the black portions 34 of the image formed on the diffusing plate must be larger than the rate of the width of the black matrix on the LCD panel. In order to increase the width of each of the black portions 34, some methods are considered. For example, the ratio of each of pixel apertures on the LCD panel is reduced, and black stripes are formed on the diffusing plate.
However, the methods are methods for intercepting light from the light source in the image projector. If the methods of intercepting light are used, therefore, the utilization efficiency of the light from the light source in the image projector is reduced, whereby the maximum brightness per one pixel which can be viewed is decreased.
In the prior art, therefore, the width of each of the black portions on the diffusing plate cannot be increased while maintaining sufficiently high brightness, whereby the most suitable condition under which a three-dimensional image is viewed in the parallax barrier method cannot be satisfied.